Laser annealing method and semiconductor device fabricating method

ABSTRACT

When the second harmonic of a YAG laser is irradiated onto semiconductor films, concentric-circle patterns are observed on some of the semiconductor films. This phenomenon is due to the non-uniformity of the properties of the semiconductor films. If such semiconductor films are used to fabricate TFTs, the electrical characteristics of the TFTs will be adversely influenced. A concentric-circle pattern is formed by the interference between a reflected beam  1  reflected at a surface of a semiconductor film and a reflected beam  2  reflected at the back surface of a substrate. If the reflected beam  1  and the reflected beam  2  do not overlap each other, such interference does not occur. For this reason, a laser beam is obliquely irradiated onto the semiconductor film to solve the interference. The properties of a crystalline silicon film formed by this method are uniform, and TFTs which are fabricated by using such crystalline silicon film have good electrical characteristics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of annealing a semiconductorfilm by using a laser beam (hereinafter referred to as laser annealing).The invention also relates to a semiconductor device fabricating methodwhich includes the laser annealing method as one step. Incidentally, theterm “semiconductor device” used herein generally denotes devices whichcan function by using semiconductor characteristics, and encompasseselectrooptical devices such as liquid crystal display devices andluminescent devices as well as electronic equipment including theelectrooptical devices as constituent parts.

2. Background Art

In recent years, a wide range of researches have been made as to the artof applying laser annealing to a semiconductor film formed on aninsulating substrate such as a glass substrate to crystallize thesemiconductor film or to improve the crystallinity thereof. Silicon iswidely used for such a semiconductor film. In the present specification,means for crystallizing a semiconductor film by a laser beam to obtain acrystalline semiconductor film is referred to as laser crystallization.

As compared with synthetic quartz glass substrates which have heretoforewidely been used, glass substrates have the advantages of beinginexpensive and rich in workability and of facilitating fabrication oflarge-area substrates. This is the reason why a wide range of researcheshave been made. The reason why lasers are preferentially used forcrystallization is that the melting points of glass substrates are low.Lasers can give high energy to semiconductor films without increasingthe temperatures of substrates to a great extent. In addition, lasersare remarkably high in throughput compared to heating means usingelectric heating furnaces.

A crystalline semiconductor is made of multiple crystal grains, and isalso called a polycrystalline semiconductor film. Since a crystallinesemiconductor film formed by the application of laser annealing has highmobility, the crystalline silicon film is used to form thin filmtransistors (TFTs). The thin film transistors are widely used in amonolithic type of liquid crystal electrooptical device in which TFTsfor pixel driving and TFTs for driver circuits are fabricated on oneglass substrate.

A method of effecting laser annealing by forming a high power pulsedlaser beam such as an excimer laser beam, by an optical system, into alaser beam which becomes a spot of several cm square or a linear shapeof length 10 cm or more at an irradiation plane, and scanning the laserbeam (or relatively moving a position irradiated with the laser beamwith respect to an irradiation plane) has preferentially been usedbecause the method is high in productivity and superior in industrialterms.

Particularly when a linear laser beam is used, high productivity can berealized because the entire irradiation plane can be irradiated with thelinear laser beam by scanning in only directions perpendicular to thelengthwise direction of the linear laser beam, unlike the case where aspot-shaped laser beam is used which needs to be scanned in forward,rearward, rightward and leftward directions. The reason why the linearlaser beam is scanned in the lengthwise direction is that the lengthwisedirection is the direction of the most efficient scanning. Because ofthis high productivity, in the laser annealing method the use of alinear laser beam into which a pulse oscillation excimer laser beam isformed by an appropriate optical system is presently becoming one ofleading manufacturing techniques for semiconductor devices which arerepresented by liquid crystal devices using TFTs.

Although there are various kinds of lasers, it is general practice touse laser crystallization due to a laser beam which uses a pulseoscillation type of excimer laser as its light source (hereinafterreferred to as an excimer laser beam). The excimer laser has high powerand hence the advantage of enabling irradiation repeated at highfrequencies, and further has the advantage of exhibiting a highabsorption coefficient against silicon film.

To form the excimer laser beam, KrF (of wavelength 248 nm) and XeCl (ofwavelength 308 nm) are used as exciting gases. However, gases such as Kr(krypton) and Xe (xenon) are very expensive and encounter the problemthat as the frequency of gas replacement becomes higher, a greaterincrease in manufacturing cost is incurred.

Attachments such as a laser tube for effecting laser oscillation and agas purifier for removing unnecessary compounds generated in anoscillation process need to be replaced every two or three years. Manyof these attachments are expensive, resulting in a similar problem of anincrease in manufacturing cost.

As described above, a laser irradiation apparatus using an excimer laserbeam surely has high performance, but needs extremely complicatedmaintenance and also has the disadvantage that if the laser irradiationapparatus is used as a production-purpose laser irradiation apparatus,its running costs (which mean costs occurring during operation) becometoo high.

There is a method which uses a solid-state laser (a laser which outputsa laser beam by means of a crystal rod formed as a resonance cavity), torealize a laser irradiation apparatus which is low in running costcompared to excimer lasers as well as a laser annealing method usingsuch a laser irradiation apparatus.

A semiconductor film was irradiated by using a YAG laser which was oneof representative solid-state lasers. The output from the YAG laser wasmodulated into the second harmonic by a non-linear optical element, andthe resulting laser beam (of wavelength 532 nm) was formed into a linearlaser beam which became a linear shape at an irradiation plane. Thesemiconductor film was an amorphous silicon film of thickness 55 nmwhich was formed on a #1737 glass substrate made by CorningIncorporated, by a plasma CVD method. However, a concentric-circlepattern such as that shown in FIG. 2 was formed on the crystallinesilicon film obtained by effecting laser annealing on the amorphoussilicon film. This pattern indicates that the in-plane properties of thecrystalline silicon film is non-uniform. Accordingly, if a TFT isfabricated from a crystalline silicon film on which a concentric-circlepattern is formed, the electrical characteristics of the TFT isadversely affected. Incidentally, in the present specification, apattern such as that shown in FIG. 2 is called a concentric-circlepattern.

SUMMARY OF THE INVENTION

The invention generally provides a laser annealing method using a laserirradiation apparatus which is low in running cost compared to relatedarts, and specifically provides a laser annealing method which does notform or can reduce a concentric-circle pattern, as well as asemiconductor device fabricating method which includes the laserannealing method as one step.

First of all, consideration is given to a cause which forms aconcentric-circle pattern such as that shown in FIG. 2. The laser beamirradiated onto the amorphous silicon film was a linear laser beam whichbecame a linear shape at the irradiation plane. For this reason, even ifany pattern is formed on the crystalline silicon film obtained afterirradiation with the laser beam, the pattern should become a patternparallel or perpendicular to the linear laser beam as long as thesemiconductor film, the substrate and a substrate stage are completelyflat. However, since the pattern observed in FIG. 2 has the shape of aconcentric circle, it may be considered that the pattern is not due tothe linear laser beam. In other words, it can be determined that thecause of the occurrence of the concentric-circle pattern lies in thedistortion of any one or plural ones of the semiconductor film, thesubstrate and the substrate stage.

The concentric-circle pattern observed in FIG. 2 is similar to Newton'srings. Newton's rings are a fringe pattern which is formed when lightsreflected from plural reflection surfaces interfere with one another.From this fact, it can be inferred that the concentric-circle pattern issimilarly due to the interference of lights reflected from pluralreflection surfaces. Experiments for identifying the plural reflectionsurfaces were performed.

FIGS. 3A and 3B respectively show the reflectivity and thetransmissivity of an amorphous silicon film (of thickness 55 nm) againstwavelengths. The amorphous silicon film is formed on the 1737 substrateby a plasma CVD method. It can be seen from FIGS. 3A and 3B that thereflectivity and the transmissivity are, respectively, 26% and 38% withrespect to the second harmonic (of wavelength 532 nm) of the YAG laser.In other words, it can be considered that since the reflectivity and thetransmissivity of the amorphous silicon film are high, an interferenceoccurs between a beam reflected from the surface of the amorphoussilicon film and a reflected beam which occurs when a laser beamtransmitted through the amorphous silicon film is reflected at a certainsurface.

The number of surfaces (reflection surfaces) at which the secondharmonic of the YAG laser transmitted through the amorphous silicon filmcan be reflected can be considered to be three as follows:

(A) the substrate stage,

(B) the back surface of the substrate, and

(C) the interface between the amorphous silicon film and the substrate.

In order to identify which of these reflection surfaces is the cause ofthe concentric-circle pattern, the first and second experiments ofeliminating the influence of each of the reflected beams were performedand a theoretical expression is obtained from the results of the firstand second experiments. In each of the first and second experiments, a55-nm-thick amorphous silicon film which was formed on a 1737 glasssubstrate 5 inches square and 0.7 mm thick was used as a semiconductorfilm. Incidentally, in the specification, the surface of the substrateis defined as a surface on which the film is deposited, while the backsurface of the substrate is defined as a surface which is opposite tothe surface on which the film is deposited.

First, the experiment of eliminating the influence of a beam reflectedfrom a substrate stage 41 was performed as the first experiment. Thefirst experiment will be described below with reference to FIG. 4. Asshown in FIG. 4, a silicon wafer 43 was obliquely disposed between thesubstrate stage 41 and a substrate 10 on which a semiconductor film 11was deposited, so that a beam reflected from the substrate stage 41 wasprevented from interfering with a reflected beam 45 from a surface ofthe semiconductor film 11, and in this state, laser annealing wasperformed. The reference numeral 44 is an incident beam, and thereference numeral 46 is a reflected beam from a surface of the siliconwafer 43. In addition, a similar experiment was performed with thesilicon wafer 43 omitted, in order to discriminate between a phenomenondue to the fact that the substrate stage 41 and the substrate 10 are notin contact with each other and a phenomenon due to the fact that thesilicon wafer 43 is obliquely disposed between the substrate stage 41and the substrate 10.

FIGS. 5A and 5B are views showing one example of the results of thefirst experiment. FIG. 5A shows different crystalline silicon films, oneof which was obtained when laser annealing was performed with thesilicon wafer 43 being obliquely disposed 4 cm apart from the substratestage 41 and the other of which was obtained when laser annealing wasperformed with the silicon wafer 43 being not disposed. FIG. 5B is aschematic view of FIG. 5A. From FIGS. 5A and 5B, it can be seen that theconcentric-circle patterns appear irrespective of the presence orabsence of the silicon wafer 43. From this fact, it can be seen that theconcentric-circle patterns are independent of the beam reflected fromthe substrate stage 41.

Then, the experiment of eliminating the influence of a beam reflectedfrom the back surface of the substrate 10 was performed as the secondexperiment. The second experiment will be described below with referenceto FIG. 6. As shown in FIG. 6, the substrate 10 was inclined withrespect to an incident beam 64 so that a reflected beam 66 from the backsurface of the substrate stage 41 and a reflected beam 65 from thesurface of the semiconductor film 11 do not interfere with each other,and laser annealing was performed in this state. Incidentally, a support42 was disposed on the substrate stage 41, and the substrate 10 wasinclined in the state of being set against the support 42. The angle ofthe incident beam 64 was changed by changing the height of the support42.

FIGS. 7A and 7B are views showing the result of the second experiment.FIG. 7A shows different crystalline silicon films which wererespectively obtained when laser annealing was performed with supports 5mm, 10 mm and 15 mm high being disposed, and FIG. 7B is a schematic viewof FIG. 7A. From FIGS. 7A and 7B, it can be seen that aconcentric-circle pattern was observed when one side of the substrate 10was set against the support 5 mm high, whereas a concentric-circlepattern vanished when one side of the substrate 10 was set against thesupport 10 mm high. In other words, it is seen that if the incidentlaser beam is inclined at an angle, the concentric-circle patterndisappears when the angle of inclination is greater than or equal to acertain angle.

The interference between a beam reflected from the surface of thesemiconductor film and a beam reflected from the interface of thesemiconductor film and the substrate will be considered below withreference to FIG. 8. The amorphous silicon film is assumed to be a plainparallel plate having a refractive index n. A laser beam 84 incident onthe amorphous silicon film at an angle θ₁ is refracted and travels at anangle θ₂ in the plain parallel plate. It is assumed here that therespective refractive indices of the amorphous silicon film and thesubstrate are 4 and 1.5 against the second harmonic (of wavelength 532nm) of the YAG laser. Owing to the difference between both refractiveindices, a phase deviation does not occur at the surface of theamorphous silicon film, but a relative phase deviation of π occurs atthe interface between the amorphous silicon film and the substrate.Taking this fact into account, a minimum condition for a reflected beamA 85 and a reflected beam B 86 is found as follows:2nd×cos θ₂ =mλ, (m is an integer).  (1)In Expression (1), λ represents the wavelength the incident beam, nrepresents the refractive index of the amorphous silicon film at thewavelength λ, and d represents the thickness of the amorphous siliconfilm. The following specific values are substituted into Expression (1):

n=4,

d=55 [nm], and

λ=532 [nm].

Substituting these values, the following expression is obtained:

$\begin{matrix}\begin{matrix}{{\cos\;\theta_{2}} = {m \times {532/\left( {2 \times 4 \times 55} \right)}}} \\{= {m \times {532/440.}}}\end{matrix} & (2)\end{matrix}$

From Expression (2), it is seen that since m can only take on θ, θ₂ canonly take on one value to minimize the interference between thereflected beam A 85 and the reflected beam B 86. From the fact thatinterference fringes occur in the case where m can take on pluralvalues, it is seen that there is no possibility that a fringe patternmade of alternate dark and bright fringes is formed from the beamreflected at the interface between the amorphous silicon film and thesubstrate.

From the above-described experiment results and theoretical expression,it can be determined that the cause of the formation of theconcentric-circle pattern is the interference between the beam reflectedfrom the surface of the amorphous silicon film and the beam reflectedfrom the back surface of the substrate. The cause that theconcentric-circle pattern was formed can be considered to be that thesubstrate was warped not in only one direction but in two differentdirections. If the substrate is distorted in only one direction like acylindrical lens, a concentric-circle pattern will not appear, and aparallel fringe pattern will be formed. FIGS. 10A and 10B are viewsshowing the result obtained when the distortion of a 1737 glasssubstrate was measured after having been heat-treated at a temperatureof 640° C. for five hours. In FIG. 10A, the horizontal axis representsthe x direction, whereas in FIG. 10B, the horizontal axis represents they direction, and the vertical axis of each FIGS. 10A and 10B representsdistortion. The x direction and the y direction represented by therespective horizontal axes are determined for convenience's sake so thatthe substrate is positioned as shown in FIG. 9 with a cut called“orientation flat” being located on the top right of the substrate. FromFIGS. 10A and 10B, it is apparent that the substrate is warped in bothof the x and y directions. At present, this distortion may have aninfluence on laser annealing, but the extent of the distortion does notbecome a problem in any other step of fabricating semiconductor devicessuch as TFTs.

On the basis of the fact that, in the second experiment, noconcentric-circle pattern appeared when laser annealing was performedwith the substrate inclined, the invention provides the art ofirradiating a laser beam onto a substrate at an angle. In accordancewith the invention, it is possible to remove or reduce thenon-uniformity of the properties of individual semiconductor films dueto the interference of laser beams. By fabricating a TFT by using such acrystalline semiconductor film, it is possible to obtain a TFT havinggood electrical characteristics.

It is desirable that the laser beam used in the invention be irradiatedin the state of being linearly formed by an optical system.Incidentally, linearly forming the laser beam means that the laser beamis formed so that it becomes linear in shape at an irradiation plane. Inaddition, the term “linear” used herein does not mean “a line” in thestrict sense, and means a rectangle having a large aspect ratio (or anellipse). For example, the term “linear” indicates a shape having anaspect ratio of 10 or more (preferably, 100-10,000).

The solid-state laser may use a generally known type of laser such as aYAG laser (ordinarily, an Nd:YAG laser), an Nd:YLF laser, an Nd:YVO₄laser, an Nd:YAIO₃ laser, a ruby laser, an alexandrite laser or aTi:sapphire laser. In particular, YVO₄ and YAG lasers which are superiorin coherence and pulse energy are preferable.

However, the laser must be of a wavelength which can be transmittedthrough the semiconductor film, because the beam reflected from the backsurface of the substrate interferes with the beam reflected at thesurface of the semiconductor film. FIG. 3B shows the transmissivity ofan amorphous silicon film of thickness 55 nm against wavelengths. FromFIG. 3B, it is seen that the laser beam must have a wavelength of 350 nmor more (preferably, 400 nm or more) so that it can be transmittedthrough the amorphous silicon film of thickness 55 nm. However, in theinvention, the material of the semiconductor film is not particularlylimited, and not only silicon but a compound semiconductor film havingan amorphous structure made of a silicon germanium (SiGe) alloy or thelike may also be applied to the invention. The wavelength may beappropriately determined by an operator because wavelengths which can betransmitted through semiconductor films differ according to the kinds,the thicknesses or the like of individual semiconductor films.

For example, if the YAG laser is to be used, since the basic wave of theYAG laser has a long wavelength of 1064 nm, it is preferable to use thesecond harmonic (of wavelength 532 nm). The first harmonic can bemodulated into the second harmonic, the third harmonic or the fourthharmonic by a wavelength modulator including non-linear elements. Theformation of each of the harmonics may conform to known arts.Incidentally, it is herein assumed that a “laser beam which uses asolid-state laser as its light source” contains not only the firstharmonic but other harmonics which are wavelength-modulated halfway onan optical path.

Otherwise, a Q-switching method (Q-modulation switching method) which iswidely used in YAG-lasers may also be used. The Q-switching method is amethod of outputting a pulsed laser having a very high energy level andsteep pulse edges by keeping the Q of a laser resonator at a fully lowvalue and suddenly increasing the Q to a high value. The Q-switchingmethod is a known art.

Any of the solid-state lasers used in the invention is capable ofoutputting a laser beam by basically using a solid-state crystal, aresonance mirror and a light source for exciting the solid-statecrystal, so that the solid-state lasers do not need extremelycomplicated maintenance unlike excimer lasers. In other words, thesolid-state lasers are very low in running cost compared to excimerlasers, and make it possible to greatly reduce the manufacturing costsof semiconductor devices. In addition, as the number of times ofmaintenance cycles decreases, the operation rate of production linesincreases, so that the overall throughput of manufacturing processesincreases, thus greatly contributing to a reduction in the manufacturingcosts of semiconductor devices. Moreover, since the areas occupied bythe solid-state lasers are small compared to excimer lasers, thesolid-state lasers are advantageous to designing of manufacturing lines.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily appreciated and understood fromthe following detailed description of preferred embodiments of theinvention when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a view showing one example of the construction of a laserirradiation apparatus;

FIG. 2 is a view showing one example of a concentric-circle pattern;

FIG. 3A is a view showing the reflectivity of an amorphous silicon film(of thickness 55 nm) against wavelengths;

FIG. 3B is a view showing the transmissivity of the amorphous siliconfilm (of thickness 55 nm) against wavelengths;

FIG. 4 is a view showing the manner in which laser annealing isperformed with the influence of a substrate stage being eliminated;

FIGS. 5A and 5B are views showing one example of the results of thelaser annealing performed with the influence of the substrate stagebeing eliminated;

FIG. 6 is a view showing the manner in which laser annealing isperformed with the influence of the back surface of the substrate stagebeing eliminated;

FIGS. 7A and 7B are views showing one example of the results of thelaser annealing performed with the influence of the back surface of thesubstrate stage being eliminated;

FIG. 8 is a view aiding in considering the interference between a beamreflected from a surface of a semiconductor film and a beam reflectedfrom the interface of the semiconductor film and a substrate;

FIG. 9 is an explanatory view of the x and y directions of thesubstrate;

FIG. 10A is a view showing an example of distortion relative to the xdirection of the substrate;

FIG. 10B is a view showing an example of distortion relative to the ydirection of the substrate;

FIG. 11 is a view showing one example of the laser annealing methodaccording to the invention;

FIG. 12 is a view showing another example of the laser annealing methodaccording to the invention;

FIGS. 13A to 13C are cross-sectional views showing the process offabricating pixel TFTs and TFTs for driver circuits;

FIGS. 14A to 14C are cross-sectional views showing the process offabricating the pixel TFTs and the TFTs for driver circuits;

FIGS. 15A to 15C are cross-sectional views showing the process offabricating the pixel TFTs and the TFTs for driver circuits;

FIG. 16 is a cross-sectional view showing the process of fabricating thepixel TFTs and the TFTs for driver circuits;

FIG. 17 is a top plan view showing the construction of a pixel TFT;

FIG. 18 is a cross-sectional view showing the process of fabricating anactive matrix type liquid crystal display device;

FIG. 19 is a view of a cross-sectional structure of a driver circuit anda pixel section of a light-emitting device;

FIG. 20A is a top plan view of the light-emitting device;

FIG. 20B is a view of a cross-sectional structure of a driver circuitand a pixel section of the light-emitting device;

FIGS. 21A to 21F are views showing different examples of a semiconductordevice according to the invention;

FIGS. 22A to 22D are views showing different examples of thesemiconductor device; and

FIGS. 23A to 23C are views showing different examples of thesemiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

The incident angle of a laser beam will be described below withreference to FIG. 1 in connection with preferred embodiments of theinvention which will be described later.

A laser beam with a beam width w₁ is made incident on a semiconductorfilm (a target to be irradiated). The incident angle at this time isassumed to be θ. In general, the semiconductor film is deposited to athickness of 25-80 nm, and since the semiconductor film is very thincompared to a thickness D (0.7 mm) of a glass substrate, the deviationof the optical path of the laser beam due to the semiconductor film canbe ignored. Accordingly, the laser beam transmitted through thesemiconductor film travels nearly rectilinearly toward the back surfaceof the substrate, and is reflected at the back surface of the substrate.The laser beam (reflected beam) reflected by the back surface of thesubstrate reaches the semiconductor film and exits from the substrate.During this time, if the incident beam and the reflected beam do not atall traverse each other on the semiconductor film, the interference ofthe beams does not occur in the semiconductor film. In other words, aconcentric-circle pattern is not formed.

The condition under which the concentric-circle pattern does not occuris expressed from FIG. 1 as follows:D×tan θ≧w/2,  (3)∴≧arctan(w/(2×D))  (3)where w=(w₁+w₂)/2. However, the result of the second experiment showsthat even if the incident beam and the reflected beam are not completelyseparated from each other, the concentric-circle pattern can be reduced.Therefore, assuming that D=0.7 [mm], tan θ=5/126 and w₁=w₂=w=0.4 [mm],the condition under which the concentric-circle pattern can be reducedis calculated as follows:0.7×5/126≧0.4/x, (x is an integer)∴x≧14.4.However, x is a denominator and can only take on an integer, so thatx≧14.Accordingly, the condition under which the concentric-circle patterndoes not occur, which condition is obtained from the experiment,becomes:D×tan θ≧w/14,  (4)∴θ≧arctan(w/(14×D)).  (4)′

If the semiconductor film is annealed with the laser beam made incidentat the angle θ which satisfies this condition, the concentric-circlepattern which would have so far been formed on the semiconductor filmcan be reduced, whereby a good crystalline semiconductor film can beformed. A TFT which is fabricated by using this crystallinesemiconductor film has good electrical characteristics. Incidentally, inthe specification, the angle θ indicates a deviation from a directionperpendicular to the substrate.

Embodiment 1

Embodiment 1 of the invention will be described below with reference toFIGS. 11 and 13A.

First of all, as a substrate 300, a substrate having transparency isprepared which is made of glass such as barium boro-silicate glass oralumina boro-silicate glass represented by the #7059 glass or the #1737glass of Corning Incorporated. Incidentally, as the substrate 300, aquartz substrate or a silicon substrate may also be used. Otherwise, aplastic substrate which has heat resistance to the treatment temperatureused in Embodiment 1 may also be used. In Embodiment 1, a glasssubstrate was prepared which was made of the #1737 glass of CorningIncorporated and was 126 mm square and 0.7 mm thick.

Then, a base film 301 made of an insulating film such as a silicon oxidefilm, a silicon nitride film or a silicon nitride oxide film is formedon the substrate 300. In Embodiment 1, the base film 301 may use atwo-layer structure, but may also use a single-layer film made of anyone of the insulating films or a structure in which two or more of theinsulating films are stacked. As the first layer of the base film 301, asilicon nitride oxide film 301 a deposited by a plasma CVD method usingSiH₄, NH₃ and N₂O as reaction gases is formed to a thickness of 10-200nm (preferably, 50-100 nm). In Embodiment 1, the silicon nitride oxidefilm 301 a of thickness 50 nm was formed (composition ratio: Si=32%,O=27%, N=24% and H=17%). Then, as the second layer of the base film 301,a silicon nitride oxide film of thickness 50-200 nm (preferably, 100-150nm) is formed to be stacked on the first layer, by a plasma CVD methodusing SiH₄ and N₂O as reaction gases. In Embodiment 1, a silicon nitrideoxide film 401 b of thickness 100 nm was formed (composition ratio:Si=32%, O=59%, N=7% and H=2%).

Then, a semiconductor film 302 is formed over the substrate 300. As thesemiconductor film 302, a semiconductor film having an amorphousstructure is formed to a thickness of 25-80 nm (preferably, 30-60 nm) bya known method (a sputtering method, an LPCVD method or a plasma CVDmethod). Although the material of the semiconductor film is notparticularly limited, it is preferable to form the semiconductor filmfrom silicon, a silicon germanium (SiGe) alloy or the like. InEmbodiment 1, an amorphous silicon film of thickness 55 nm was depositedby using a plasma CVD method.

Incidentally, in Embodiment 1, after the base insulating film such as asilicon nitride film or a silicon nitride oxide film has been formed onthe substrate, the semiconductor film is formed. In the case where thesemiconductor film is formed after the base insulating film has beenformed on the substrate, the number of surfaces by which the laser beamis to be reflected increases. However, since the respective refractiveindices of the substrate and the base insulating film are nearly thesame as each other, a variation in refractive index at the interfacebetween the base insulating film and the substrate can be ignored.

Then, crystallization of the semiconductor film is performed.Crystallization using a laser annealing method is applied to thecrystallization of the semiconductor film. As methods of crystallizingthe semiconductor film, there are a thermal crystallization method and athermal crystallization method using a catalyst such as nickel, inaddition to crystallization using a laser annealing method. Otherwise,any one of these crystallization methods and a laser annealing methodmay be combined. The invention is applied to and embodied in lasercrystallization.

In the crystallization using a laser annealing method, it is desirablethat hydrogen contained in the amorphous semiconductor film bedischarged in advance. Specifically, it is preferable to reduce thehydrogen content to 5 atom % or less by exposing the amorphoussemiconductor film to a nitrogen atmosphere at 400-500° C. forapproximately one hour. In this manner, the laser resistance of the filmis remarkably improved.

An optical system for the laser beam will be described below withreference to FIG. 11. As a laser oscillator 201, it is desirable to usea high-power, continuous- or pulse-oscillation solid-state laser (a YAGlaser, a YVO₄ laser, a YLF laser, a YAIO₃ laser, a ruby laser, analexandrite laser, a Ti:sapphire laser or the like). Of course, a gaslaser, a glass laser or the like may also be used as long as it has highpower. The laser light generated from the laser oscillator 201 is formedinto a linear beam whose irradiation plane has a linear shape, by usingthe optical system. The optical system uses, for example, a long focallength cylindrical lens 205 for enlarging a laser beam into a long beam,and a cylindrical lens 206 for converging a laser beam into a thin beam.By using such long focal length cylindrical lenses, it is possible toobtain a laser beam which is reduced in aberration and is uniform inenergy distribution at or near the irradiation plane. In addition, thelong focal length cylindrical lenses are effective in restraining aremarkable difference from occurring between the beam width of a beamincident on the semiconductor film and the beam width of a beamreflected from the back surface of the substrate. Experiments of thepresent inventor showed that when a cylindrical lens having a focallength of 500 mm or more was used, the influence of aberration was ableto be drastically reduced.

A reflecting mirror 207 is provided in front of the cylindrical lens 206so that the traveling direction of the laser beam can be changed. Theangle at which the laser beam is made incident on the irradiation planecan be adjusted to the desired angle θ by the reflecting mirror 207. Ifthe angle of the cylindrical lens 206 is changed according to the angleof the reflecting mirror 207, a laser beam having far higher symmetrycan be formed on the irradiation plane.

In addition, when linear beams are to be irradiated onto a semiconductorfilm, the linear beams may also be irradiated with an overlap percentageof 50-98% or without overlap. Since optimum conditions differ accordingto the states of semiconductor films or the delay periods of laserbeams, it is preferable that an operator appropriately determine theoptimum conditions.

In Embodiment 1, a YAG laser was used as the laser oscillator 201. Theoutput from the YAG laser was modulated into the second harmonic by anon-linear optical element 202 and was then formed into a linear beam oflength 130 mm and width 0.4 mm by using the optical system, and thelinear beam was irradiated onto the semiconductor film. At this time,the linear beam was irradiated with an angular deviation of 5 degreesfrom the direction perpendicular to the substrate. Since the cylindricallens 206 having a long focal length was used, w₁=w₂=w=0.4 [mm] may beused. If the irradiation condition of Embodiment 1 is applied toExpression (4), the left-hand side becomes:0.7×tan 5=0.0612,and the right-hand side becomes:0.4/8=0.0500.Accordingly, Expression (4) is satisfied, and a concentric-circlepattern was not observed on the crystalline semiconductor film obtainedby the laser annealing. A TFT which is fabricated by using thiscrystalline semiconductor film has good electrical characteristics.

Embodiment 2

Embodiment 2 which differs from Embodiment 1 will be described belowwith reference to FIG. 12.

A substrate and a semiconductor film were fabricated in accordance withthe process of Embodiment 1. In Embodiment 2 as well, a #1737 glasssubstrate made by Corning Incorporated was used, and an amorphoussilicon film (of thickness 55 nm) was formed over the glass substrate bya CVD method.

The optical system of Embodiment 2 will be described below withreference to FIG. 12. In FIG. 12, the same reference numerals are usedto denote parts corresponding to those used in the optical system shownin FIG. 11. In Embodiment 2, the reflecting mirror 207 is fixed at 45degrees with respect to the laser beam, and a substrate stage 203 isinclined by an angle θ from the horizontal direction.

In Embodiment 2, a YAG laser was used as the laser oscillator 201. Theoutput from the YAG laser was modulated into the second harmonic by thenon-linear optical element 202 and was then formed into a linear beam oflength 130 mm and width 0.4 mm by using the optical system, and thelinear beam was irradiated onto the semiconductor film. At this time,the linear beam was irradiated with an angular deviation of 10 degreesfrom the direction perpendicular to the substrate. Since the cylindricallens 206 having a long focal length was used, w₁=w₂=w=0.4 [mm] may beused. If the irradiation condition of Embodiment 1 is applied toExpression (4), the left-hand side becomes:0.7×tan 10=0.1234and the right-hand side becomes:0.4/8=0.0500.Accordingly, Expression (4) is satisfied, and a concentric-circlepattern was not observed on the crystalline semiconductor film obtainedby the laser annealing. A TFT which is fabricated by using thiscrystalline semiconductor film has good electrical characteristics.

Embodiment 3

In this embodiment, the manufacturing method of the active matrixsubstrate is explained using FIGS. 13 to 21.

First, in this embodiment, a substrate 300 is used, which is made ofglass such as barium borosilicate glass or aluminum borosilicate,represented by such as Corning #7059 glass and #1737 glass. Note that,as the substrate 300, a quartz substrate, a silicon substrate, ametallic substrate or a stainless substrate on which is formed aninsulating film. A plastic substrate with heat resistance to a processtemperature of this embodiment may also be used.

Then, a base film 301 formed of an insulating film such as a siliconoxide film, a silicon nitride film or a silicon oxynitride film isformed on the substrate 300. In this embodiment, a two-layer structureis used as the base film 301. However, a single-layer film or alamination structure consisting of two or more layers of the insulatingfilm may be used. As a first layer of the base film 301, a siliconoxynitride film 301 a is formed with a thickness of 10 to 200 nm(preferably 50 to 100 nm) with a plasma CVD method using SiH₄, NH₃, andN₂O as reaction gas. In this embodiment, the silicon oxynitride film 301a (composition ratio Si=32%, O=27%, N=24% and H=17%) with a filmthickness of 50 nm is formed. Then, as a second layer of the base film301, a silicon oxynitride film 301 b is formed and laminated into athickness of 50 to 200 nm (preferably 100 to 150 nm) with a plasma CVDmethod using SiH₄ and N₂O as reaction gas. In this embodiment, thesilicon oxynitride film 401 b (composition ratio Si=32%, O=59%, N=7% andH=2%) with a film thickness of 100 nm is formed.

Subsequently, semiconductor layer 302 are formed on the base film. Thesemiconductor layer 302 are formed from a semiconductor film with anamorphous structure which is formed by a known method (such as asputtering method, an LPCVD method, or a plasma CVD method) into thethickness of from 25 to 80 nm (preferably 30 to 60 nm). The material ofthe semiconductor film is not particularly limited, but it is preferableto be formed of silicon, a silicon germanium (SiGe) alloy, or the like.In this embodiment, 55 nm thick amorphous silicon film is formed by aplasma CVD method.

Next, the crystallization of the semiconductor film is conducted. Thelaser crystallization is applied to the crystallization of thesemiconductor film. Further, other than laser crystallization, thermalcrystallization or thermal crystallization using nickel as a catalystare applicable for a crystallization of the semiconductor film. Thecrystallization of the semiconductor film is subjected by a method ofcombination in which laser crystallization and one of thesecrystallization methods above. The laser crystallization is implementedby applying the present invention. For example, the laser light, bywhich a solid laser (YAG laser, YVO₄ laser, YLF laser, YaIO₃ laser, rubylaser, alexandrite laser, Ti:sapphire laser, glass laser or the like) isset as a light source, is processed in to a linear beam. The laser lightis irradiated to the semiconductor film by using a method shown in FIG.11 or 12. In this embodiment, after the substrate is exposed in thenitrogen atmosphere of 500° C. temperature for 1 hour, thecrystallization of the semiconductor film is conducted by the laserannealing shown in FIG. 11, whereby the crystalline silicon film havingthe crystal grains of large grain size is formed. Here, the YAG laser isused for the laser oscillator. The laser light modulated into the secondharmonic by nonlinear optical element is processed into the linear beamby an optical system and irradiated to the semiconductor film. When thelinear beam is irradiated to the semiconductor film, although theoverlap ratio can be set from 50 to 98%, the ratio may be set suitablyby the operator because the optimum conditions are different accordingto the state of the semiconductor film and the wavelength of the laserlight.

Thus formed the crystalline semiconductor film is patterned into thedesired shape to form the semiconductor layers 402 to 406. In thisembodiment, the crystalline silicon film is patterned by using thephotolithography to form the semiconductor layers 402 to 406.

Further, after the formation of the semiconductor layers 402 to 406, aminute amount of impurity element (boron or phosphorus) may be doped tocontrol a threshold value of the TFT.

A gate insulating film 407 is then formed for covering the semiconductorlayers 402 to 406. The gate insulating film 407 is formed of aninsulating film containing silicon by a plasma CVD method or asputtering method into a film thickness of from 40 to 150 nm. In thisembodiment, the gate insulating film 407 is formed of a siliconoxynitride film into a thickness of 110 nm by a plasma CVD method(composition ratio Si=32%, O=59%, N=7%, and H=2%). Of course, the gateinsulating film is not limited to the silicon oxynitride film, and another insulating film containing silicon may be used as a single layeror a lamination structure.

Besides, when the silicon oxide film is used, it can be possible to beformed by a plasma CVD method in which TEOS (tetraethyl orthosilicate)and O₂ are mixed and discharged at a high frequency (13.56 MHz) powerdensity of 0.5 to 0.8 W/cm² with a reaction pressure of 40 Pa and asubstrate temperature of 300 to 400° C. Good characteristics as the gateinsulating film can be obtained in the manufactured silicon oxide filmthus by subsequent thermal annealing at 400 to 500° C.

Then, as shown in FIG. 13B, on the gate insulating film 407, a firstconductive film 408 with a thickness of 20 to 100 nm and a secondconductive film 409 with a thickness of 100 to 400 nm are formed andlaminated. In this embodiment, the first conductive film 408 of TaN filmwith a film thickness of 30 nm and the second conductive film 409 of a Wfilm with a film thickness of 370 nm are formed into lamination. The TaNfilm is formed by sputtering with a Ta target under a nitrogencontaining atmosphere. Besides, the W film is formed by the sputteringmethod with a W target. The W film may be formed by a thermal CVD methodusing tungsten hexafluoride (WF₆). Whichever method is used, it isnecessary to make the material have low resistance for use as the gateelectrode, and it is preferred that the resistivity of the W film is setto less than or equal to 20 μΩcm. By making the crystal grains large, itis possible to make the W film have lower resistivity. However, in thecase where many impurity elements such as oxygen are contained withinthe W film, crystallization is inhibited and the resistance becomeshigher. Therefore, in this embodiment, by forming the W film by asputtering method using a W target with a high purity of 99.9999% and inaddition, by taking sufficient consideration to prevent impuritieswithin the gas phase from mixing therein during the film formation, aresistivity of from 9 to 20 μΩcm can be realized.

Note that, in this embodiment, the first conductive film 408 is made ofTaN, and the second conductive film 409 is made of W, but the materialis not particularly limited thereto, and either film may be formed of anelement selected from the group consisting of Ta, W, Ti, Mo, Al, Cu, Cr,and Nd, or an alloy material or a compound material containing the aboveelement as its main constituent. Besides, a semiconductor film, typifiedby a polycrystalline silicon film doped with an impurity element such asphosphorus, may be used. Further, an AgPdCu alloy may be used. Besides,any combination may be employed such as a combination in which the firstconductive film is formed of tantalum (Ta) and the second conductivefilm is formed of W, a combination in which the first conductive film isformed of titanium nitride (TiN) and the second conductive film isformed of W, a combination in which the first conductive film is formedof tantalum nitride (TaN) and the second conductive film is formed ofAl, or a combination in which the first conductive film is formed oftantalum nitride (TaN) and the second conductive film is formed of Cu.

Next, masks 410 to 415 made of resist are formed using aphotolithography method, and a first etching process is performed inorder to form electrodes and wirings. This first etching process isperformed with the first and second etching conditions. In thisembodiment, as the first etching conditions, an ICP (inductively coupledplasma) etching method is used, a gas mixture of CF₄, Cl₂ and O₂ is usedas an etching gas, the gas flow rate is set to 25/25/10 sccm, and plasmais generated by applying a 500 W RF (13.56 MHz) power to a coil shapeelectrode under 1 Pa. A dry etching device with ICP (Model E645-□ICP)produced by Matsushita Electric Industrial Co. Ltd. is used here. A 150W RF (13.56 MHz) power is also applied to the substrate side (test piecestage) to effectively apply a negative self-bias voltage. The W film isetched with the first etching conditions, and the end portion of thefirst conductive layer is formed into a tapered shape.

Thereafter, the first etching conditions are changed into the secondetching conditions without removing the masks 410 to 415 made of resist,a mixed gas of CF₄ and Cl₂ is used as an etching gas, the gas flow rateis set to 30/30 sccm, and plasma is generated by applying a 500 W RF(13.36 MHz) power to a coil shape electrode under 1 Pa to therebyperform etching for about 30 seconds. A 20 W RF (13.56 MHz) power isalso applied to the substrate side (test piece stage) to effectively anegative self-bias voltage. The W film and the TaN film are both etchedon the same order with the second etching conditions in which CF₄ andCl₂ are mixed. Note that, the etching time may be increased byapproximately 10 to 20% in order to perform etching without any residueon the gate insulating film.

In the first etching process, the end portions of the first and secondconductive layers are formed to have a tapered shape due to the effectof the bias voltage applied to the substrate side by adopting masks ofresist with a suitable shape. The angle of the tapered portions may beset to 15° to 45°. Thus, first shape conductive layers 417 to 422 (firstconductive layers 417 a to 422 a and second conductive layers 417 b to422 b) constituted of the first conductive layers and the secondconductive layers are formed by the first etching process. Referencenumeral 416 denotes a gate insulating film, and regions of the gateinsulating film which are not covered by the first shape conductivelayers 417 to 422 are made thinner by approximately 20 to 50 nm byetching.

Then, a first doping process is performed to add an impurity element forimparting an n-type conductivity to the semiconductor layer withoutremoving the mask made of resist (FIG. 14A). Doping may be carried outby an ion doping method or an ion injection method. The condition of theion doping method is that a dosage is 1×10¹³ to 5×10¹⁵/cm², and anacceleration voltage is 60 to 100 keV. In this embodiment, the dosage is1.5×10¹⁵/cm² and the acceleration voltage is 80 keV. As the impurityelement for imparting the n-type conductivity, an element which belongsto group 15 of the periodic table, typically phosphorus (P) or arsenic(As) is used, and phosphorus is used here. In this case, the conductivelayers 417 to 422 become masks to the impurity element for imparting then-type conductivity, and high concentration impurity regions 306 to 310are formed in a self-aliening manner. The impurity element for impartingthe n-type conductivity is added to the high concentration impurityregions 306 to 310 in the concentration range of 1×10²⁰ to 1×10²¹/cm³.

Thereafter, a second etching process is performed without removing themasks made of resist. A mixed gas of CF₄, Cl₂ and O₂ may be used asetching gas and the W film is selectively etched. The second conductivelayers 428 b to 433 b are formed by a second etching process. On theother hand, the first conductive layers 417 a to 422 a are hardlyetched, and the second conductive layers 428 to 433 are formed.

Next, a second doping process is performed as shown in FIG. 14B withoutremoving the masks from resists. The impurity elements which impartsn-type conductivity is doped under the condition that the dose amount islower than that of a first doping process with an acceleration voltage70 to 120 keV. In this embodiment, the dosage is 1.5×10¹⁴/cm², and theacceleration voltage is 90 keV. The second doping process is using asecond shaped conductive layers 428 to 433 as masks, and the impurityelements is doped with a semiconductor layer at the below of the secondconductive layers 428 b to 433 b. The second high concentration impurityregions 423 a to 427 a and low concentration impurity region 423 b to427 b are newly formed.

Next, after the masks are removed, masks 434 a and 434 b from resistsare newly formed, and the third etching process is performed as shown inFIG. 14C. A mixed gas of SF₆, and Cl₂ is used as an etching gas, the gasflow rate is set to 50/10 sccm, and plasma is generated by applying a500 W RF (13.56 MHz) power to a coil shape electrode under 1.3 Pa tothereby perform etching for about 30 seconds. A 10 W RF (13.56 MHz)power is also applied to the substrate side (test piece stage) toeffectively applied to a negative self-bias voltage. Thus the thirdshape conductive layers 435 to 438 are formed by etching a TaN film ofthe p-channel type TFT and the TFT of the pixel portion (pixel TFT)using above-mentioned third etching process.

Next, after removing the masks from resists, the insulating layers 439to 444 are formed, removing selectively the gate insulating film 416 andusing the second shape conductive layer 428, 430 and the second shapeconductive layers 435 to 438 as a mask. (FIG. 15A)

Successively, there is carried out a third doping processing by newlyforming masks 445 a to 445 c comprising resists. By the third dopingprocessing, there are formed impurity regions 446, 447 added with animpurity element for providing a conductive type reverse to theabove-described one conductive type at semiconductor layers constitutingactivation layers of p-channel type TFTs. The impurity regions areformed self-adjustingly by adding the impurity element providing p-typeby using the second conductive layers 435 a, 438 a as masks against theimpurity element. In this embodiment, the impurity regions 446 and 447are formed by an ion doping process using diborane (B₂H₆). (FIG. 15B) Inthe third doping processing, the semiconductor layers forming n-channeltype TFTs are covered by the masks 445 a to 445 c comprising resists.Although the impurity regions 446, 447 are added with phosphorus atconcentrations different from each other by the first doping processingand the second doping process, in any of the regions, by carrying outthe doping processing such that the concentration of the impurityelement for providing p-type falls in a range of 2×10²⁰ through2×10²¹/cm³, the impurity regions function as source regions and drainregions of p-channel type TFTs and accordingly, no problem is posed. Inthis embodiment, portions of the semiconductor layers constitutingactivation layers of p-channel type TFTs are exposed and accordingly,there is achieved an advantage that the impurity element (boron) is easyto add thereto.

The impurity regions are formed at the respective semiconductor layersby the above-described steps.

Next, a first interlayer insulating film 461 is formed by removing themasks 445 a to 445 c comprising resists. The first interlayer insulatingfilm 461 is formed by an insulating film including silicon and having athickness of 100 through 200 nm by using a plasma CVD process or asputtering process. In this embodiment, a silicon oxynitride film havinga film thickness of 150 nm is formed by a plasma CVD process. Naturally,the first interlayer insulating film 461 is not limited to the siliconoxynitride film but other insulating film including silicon may be usedas a single layer or a laminated structure.

Next, as shown by FIG. 15C, there is carried out a step of activatingthe impurity elements added to the respective semiconductor layers. Theactivating step is carried out by a thermal annealing process using afurnace annealing furnace. The thermal annealing process may be carriedout in a nitrogen atmosphere having an oxygen concentration equal to orsmaller than 1 ppm, preferably, equal to or smaller than 0.1 ppm at 400through 700° C. representatively, 500 through 550° C. and in thisembodiment, the activation is carried out by a heat treatment at 550° C.for 4 hours. Further, other than the thermal annealing process, a laserannealing process or a rapid thermal annealing process (RTA process) isapplicable.

Further, when the thermal crystallization is also applied, which isusing nickel or the like as a catalyst in the crystallizing step, theimpurity regions 423 a, 425 a, 426 a, 446 a and 447 a in which thematerial elements include a high concentration of phosphorus arecrystallized simultaneously with the activation. Thereforeabove-mentioned metal elements are gettered by the above mentionedimpurity regions and a metal element concentration in the semiconductorlayer mainly constituting a channel-forming region is reduced. Accordingto TFT having the channel forming region fabricated in this way, the offcurrent value is reduced, crystalline performance is excellent andtherefore, there is provided high field effect mobility and excellentelectric properties can be achieved.

Further, the heat treatment may be carried out prior to forming thefirst interlayer insulating film. However, when a wiring material usedis weak at heat, it is preferable to carry out the activation afterforming the interlayer insulating film (insulating film whose majorcomponent is silicon, for example, silicon nitride film) for protectingwirings as in this embodiment.

Further, there is carried out a step of hydrogenating the semiconductorlayer by carrying out a heat treatment in an atmosphere including 3 to100% of hydrogen at 300 to 550° C. for 1 through 12 hours. In thisembodiment, there is carried out a heat treatment in a nitrogenatmosphere including about 3% of hydrogen at 410° C. for 1 hour. Thestep is a step of terminating dangling bond of the semiconductor layerby hydrogen included in the interlayer insulating film. As other meansof hydrogenation, there may be carried out plasma hydrogenation (usinghydrogen excited by plasma).

Further, when a laser annealing is used as an activation, it ispreferable to irradiate laser beam of YAG laser or the like aftercarrying out the hydrogenation.

Next, there is formed a second interlayer insulating film 462 comprisingan inorganic insulating material or an organic insulating material abovethe first interlayer insulating film 461. In this embodiment, there isformed a acrylic resin film having film thickness of 1.6 μm and there isused a film having a viscosity of 10 to 1000 cp, preferably, 40 through200 cp and formed with projections and recesses at a surface thereof.

In this embodiment, in order to prevent the mirror reflection,projection and recess portions are formed on the surfaces of the pixelelectrodes by forming the second interlayer insulating film withprojection and recess portions on the surface. Also, in order to attainlight scattering characteristics by forming the projection and recessportions on the surfaces of the pixel electrodes, projection portionsmay be formed in regions below the pixel electrodes. In this case, sincethe same photomask is used in the formation of the TFTs, the projectionportions can be formed without increasing the number of processes. Notethat the projection portion may be suitably provided in the pixelportion region except for the wirings and the TFT portion on thesubstrate. Thus, the projection and recess portions are formed on thesurfaces of the pixel electrodes along the projection and recessportions formed on the surface of the insulating film covering theprojection portion.

Also, a film with the leveled surface may be used as the secondinterlayer insulating film 462. In this case, the following ispreferred. That is, after the formation of the pixel electrodes,projection and recess portions are formed on the surface with a processusing a known method such as a sandblast method or an etching method.Thus, since the mirror reflection is prevented and reflection light isscattered, whiteness is preferably increased.

Then, in a driver circuit 506, wirings 463 to 467 electrically connectedwith the respective impurity regions are formed. Note that those wiringsare formed by patterning a lamination film of a Ti film with a filmthickness of 50 nm and an alloy film (alloy film of Al and Ti) with afilm thickness of 500 nm.

Also, in a pixel portion 507, a pixel electrode 470, a gate wiring 469,and a connection electrode 468 are formed (FIG. 16). By this connectionelectrode 468, an electrical connection between a source wiring(lamination layer of the impurity region 443 b and the first conductivelayer 449) and the pixel TFT is formed. Also, an electrical connectionbetween the gate wiring 469 and the gate electrode of the pixel TFT isformed. With respect to the pixel electrode 470, an electricalconnection with the drain region 442 of the pixel TFT and an electricalconnection with the semiconductor layer 458 which functions as one ofelectrodes for forming a storage capacitor are formed. It is desiredthat a material having a high reflectivity, such as a film containing Alor Ag as its main constituent, or a lamination film thereof, is used forthe pixel electrode 470.

Thus, the driver circuit 506 having a CMOS circuit formed by ann-channel TFT 501 and a p-channel TFT 502 and an n-channel type TFT 503,and the pixel portion 507 having a pixel TFT 504 and a retainingcapacitor 505 can be formed on the same substrate. As a result, theactive matrix substrate is completed.

The n-channel type TFT 501 of the driver circuit 506 has a channelforming region 423 c, a low concentration impurity region (GOLD region)423 b overlapping with the first conductive layer 428 a constituting aportion of the gate electrode, and a high concentration impurity region423 a which functions as the source region or the drain region. Thep-channel type TFT 502 forming the CMOS circuit by connecting with then-channel type TFT 501 through an electrode 466 has a channel formingregion 446 d, an impurity region 446 b, 446 c formed outside the gateelectrode, and a high concentration impurity region 446 a whichfunctions as the source region or the drain region. The n-channel typeTFT 503 has a channel forming region 425 c, a low concentration impurityregion 425 b (GOLD region) overlapping with the first conductive layer430 a comprising a part of the gate electrode, and a high concentrationimpurity region 425 a which functions as the source region or the drainregion.

The pixel TFT 504 of the pixel portion includes a channel forming region426 c, a low concentration impurity region 426 b (LDD region) formedoutside the gate electrode, and the high concentration impurity region426 a functioning as a source region or a drain region. Besides,impurity elements imparting p-type conductivity are added to therespective semiconductor layers 447 a, 447 b functioning as one of theelectrodes of the storage capacitor 505. The storage capacitor 505 isformed from the electrode (a lamination of 438 a and 438 b) and thesemiconductor layers 447 a to 447 c using the insulating film 444 as adielectric member.

Further, in the pixel structure of this embodiment, an end portion ofthe pixel electrode is formed by arranging it so as to overlap with thesource wiring so that the gap between the pixel electrodes is shieldedfrom light without using a black matrix.

A top view of the pixel portion of the active matrix substratemanufactured in this embodiment is shown in FIG. 17. Note that, the samereference numerals are used to indicate parts corresponding FIGS. 13 to16. A dash line A-A′ in FIG. 16 corresponds to a sectional view takenalong the line A-A′ in FIG. 17. Also, a dash line B-B′ in FIG. 16corresponds to a sectional view taken along the line B-B′ in FIG. 17.

Thus formed active matrix substrate has a TFT which is formed by usingthe semiconductor film conducted homogeneous annealing. Therefore,enough operating characteristics and reliability of the active matrixsubstrate can be obtained.

This embodiment can be performed by freely combining with Embodiments 1to 2.

Embodiment 4

In this embodiment, a manufacturing process of a reflection type liquidcrystal display device from the active matrix substrate manufactured inaccordance with Embodiment 3 will be described hereinbelow. FIG. 18 isused for an explanation thereof.

First, in accordance with Embodiment 3, an active matrix substrate in astate shown in FIG. 17 is obtained, and thereafter, an alignment film567 is formed on the active matrix substrate of FIG. 17, at least on thepixel electrode 470, and is subjected to a rubbing process. Note that,in this embodiment, before the formation of the alignment film 567, aspacer 572 for maintaining a gap between the substrates is formed at adesired position by patterning an organic film such as an acrylic resinfilm. Further, spherical spacers may be scattered on the entire surfaceof the substrate in place of the columnar like spacer.

Next, an opposing substrate 569 is prepared. The colored layers 570, 571and a leveling film 573 are formed on the opposing substrate 569. Thered-colored layer 570 and the blue-colored layer 572 are partiallyoverlapped with each other, thereby forming a light shielding portion.Note that, the red-colored layer and a green-colored layer are partiallyoverlapped with each other, thereby forming a light shielding portion.

In this embodiment, the substrate shown in Embodiment 3 is used.Accordingly, in FIG. 17 showing a top view of the pixel portion inaccordance with Embodiment 3, light shielding must be performed at leastgaps between the gate wiring 469 and the pixel electrodes 470, a gapbetween the gate wiring 469 and the connection electrode 468, and a gapbetween the connection electrode 468 and the pixel electrode 470. Inthis embodiment, the opposing substrate and the active matrix substrateare stuck so that the light shielding portions from laminated layer ofcolored layer each other overlap with the positions which need to beshielded from light.

Like this, without using a black mask, the gaps between the respectivepixels are shielded from light by the light shielding portion. As aresult, the reduction of the manufacturing steps can be attained.

Next, the opposing electrode 576 from transparent conductive film isformed on the leveling film 573, at least on the pixel portion. Thealignment film 574 on the entire surface of the opposing substrate andthe rubbing process is performed.

Then, an active matrix substrate on which a pixel portion and a drivercircuit are formed is stuck with the opposing substrate by a sealingagent 568. In the sealing agent 568, a filler is mixed, and the twosubstrates are stuck with each other while keeping a uniform gap by theeffect of this filler and the columnar spacer. Thereafter, a liquidcrystal material 575 is injected between both the substrates toencapsulate the substrates completely by an encapsulant (notillustrated). A known liquid crystal material may be used as the liquidcrystal material 575. Thus, the reflection type liquid crystal displaydevice shown in FIG. 18 is completed. Then, if necessary, the activematrix substrate or the opposing substrate may be parted into desiredshapes. Further, a polarizing plate is adhered to only the opposingsubstrate (not illustrated). Then, an FPC is adhered using a knowntechnique.

Thus formed liquid crystal display device have a TFT which is formed byusing the semiconductor film conducted homogeneous annealing. Therefore,enough operating characteristics and reliability of the above-mentionedliquid crystal display device can be obtained. Such liquid crystaldisplay device can be used as a display portion of various electronicdevice.

This embodiment can be combined with Embodiments 1 and 3 freely.

Embodiment 5

In this embodiment, the example of manufacturing the light-emittingdevice by using manufacturing method of TFT when forming the activematrix substrate shown in Embodiment 3 is described. In thisspecification, the light-emitting device is a generic name which is adisplay panel enclosing the light-emitting element between the substrateand the cover material and the display module mounted mounting an IC onthe display panel. The light-emitting element has a light-emitting layercontaining an organic compound material which can obtain the electroluminescence generated by adding the electric field, the anode layer andthe cathode layer. Further, in the luminescence in an organic compound,the luminescence (fluorescence light) when returning from the state ofsinglet exciton to the basic state and the luminescence (phosphoruslight) when returning from the state of triplet exciton to the basicstate. Either or both luminescence are contained.

Further, in this embodiment, the organic light-emitting layer is definedall layers formed between the anode and the cathode. The organiclight-emitting layer is specifically including the light-emitting layer,the hole injection layer, the electron injection layer, the holetransport layer and the electron transport layer. Basically, thelight-emitting element have a structure which is constructed by theanode layer, the light-emitting layer and the cathode layersequentially. Additionally, the light-emitting layer may have followingtwo structures. The first structure is constructed sequentially by theanode layer, the hole injection layer, the light-emitting layer and thecathode layer. The second structure is sequentially constructed by theanode layer, the hole injection layer, the light-emitting layer, theelectron injection layer and the cathode layer.

FIG. 19 is a cross-sectional view of the light-emitting device of thepresent invention. In FIG. 19, a switching TFT 603 provided on asubstrate 700 is formed using the n-channel type TFT 503 of FIG. 19.Thus, this structure may be referred to the description of the n-channeltype TFT 503.

Note that, in this embodiment, a double gate structure in which twochannel forming regions are formed is used. However, a single gatestructure in which one channel forming region is formed, or a triplegate structure in which three channel forming regions are formed may beused.

A driver circuit provided on the substrate 700 is formed using the CMOScircuit of FIG. 19. Thus, this structure may be referred to thedescriptions of the n-channel type TFT 501 and the p-channel type TFT502. Note that, in this embodiment, the single gate structure is used.However, the double gate structure or the triple gate structure may alsobe used.

Also, wirings 701 and 703 function as a source wiring of the CMOScircuit, a wiring 702 functions as a drain wiring thereof. A wiring 704functions as a wiring for electrically connecting a source wiring 708with a source region of the switching TFT. A wiring 705 functions as awiring for electrically connecting a drain wiring 709 with a drainregion of the switching TFT.

Note that, a current-controlled TFT 604 is formed using the p-channeltype TFT 502 of FIG. 19. Thus, this structure may be referred to thedescriptions of the p-channel type TFT 502. Note that, in thisembodiment, the single gate structure is used. However, the double gatestructure or the triple gate structure may be used.

Also, a wiring 706 is a source wiring (corresponding to a current supplyline) of the current-controlled TFT. Reference numeral 707 denotes anelectrode which is electrically connected with a pixel electrode 710 byoverlapping with the pixel electrode 710 of the current-controlled TFT.

Note that, reference numeral 710 denotes the pixel electrode (anode of alight-emitting element) made from a transparent conductive film. As thetransparent conductive film, a compound of indium oxide and tin oxide, acompound of indium oxide and zinc oxide, zinc oxide, tin oxide, orindium oxide can be used. Also, the transparent conductive film to whichgallium is added may be used. The pixel electrode 710 is formed on alevel interlayer insulating film 711 before the formation of the abovewirings. In this embodiment, it is very important to level a step in theTFT using the leveling film 711 made of resin. Since a light-emittinglayer formed later is extremely thin, there is the case whereinsufficient light-emitting occurs due to the step. Thus, in order toform the light-emitting layer as level as possible, it is desired thatthe step is leveled before the formation of the pixel electrode 710.

After the wirings 701 to 707 are formed, a bank 712 is formed as shownin FIG. 19. The bank 712 may be formed by patterning an insulating filmwith a thickness of 100 to 400 nm containing silicon or an organic resinfilm.

Note that, since the bank 712 is an insulating film, it is necessary topay attention to a dielectric breakdown of an element in the filmformation. In this embodiment, a carbon particle or a metal particle isadded to the insulating film which is a material of the bank 712 toreduce a resistivity. Thus, an electrostatic occurrence is suppressed.Here, an additional amount of the carbon particle or the metal particlemay be controlled such that the resistivity is 1×10⁶ to 1×10¹² Ωm(preferably, 1×10⁸ to 1×10¹⁰ Ωm).

An EL layer 713 is formed on the pixel electrode 710. Note that, onlyone pixel is shown in FIG. 19. However, in this embodiment, thelight-emitting layers are formed corresponding to respective colors of R(red), G (green), and B (blue). Also, in this embodiment, a lowmolecular organic light-emitting material is formed by an evaporationmethod. Concretely, copper phthalocyanine (CuPc) film with a thicknessof 20 nm is provided as a hole injection layer, and atris-8-quinolinolate aluminum complex (Alq₃) film with a thickness of 70nm is provided thereon as a light-emitting layer. Thus, a laminationstructure of those films is formed. A light-emitting color can becontrolled by adding a fluorochrome such as quinacridon, perylene, orDCM1 to Alq₃.

Note that, the above example is one example of the organiclight-emitting material which can be used as the light-emitting layer,and it is unnecessary to be limited to this example. The light-emittinglayer (layer for causing light to emit and a carrier to move for theemitting of light) may be formed by freely combining the light-emittinglayer and a charge transport layer or a charge injection layer. Forexample, in this embodiment, although the example that the low molecularorganic light-emitting material is used as the light-emitting layer isshown, a polymer organic light-emitting material may be also used. Also,an inorganic material such as silicon carbide can be used as the chargetransport layer or the charge injection layer. A known material can beused as the organic light-emitting material and the inorganic material.

Next, a cathode 714 made from a conductive film is provided on thelight-emitting layer 713. In the case of this embodiment, an alloy filmof aluminum and lithium is used as the conductive film. Of course, aknown MgAg film (alloy film of magnesium and silver) may be used. As acathode material, the conductive film made of an element which belongsto group 1 or group 2 of the periodic table, or the conductive film towhich those elements are added may be used.

When this cathode 714 is formed, a light-emitting element 715 iscompleted. Note that, the light-emitting element 715 completed hererepresents a diode formed by the pixel electrode (anode) 710, thelight-emitting layer 713, and the cathode 714.

It is effective to provide a passivation film 716 so as to completelycover the light-emitting element 715. As the passivation film 716, asingle layer of an insulating film containing a carbon film, a siliconnitride film, or silicon oxynitride film, or a lamination layer of acombination with the insulating film is used.

Here, it is preferred that a film with a good coverage is used as thepassivation film, and it is effective to use the carbon film, inparticular a DLC (diamond like carbon) film. Since the DLC film can beformed in a range of a room temperature to 100° C., it can be easilyformed over the light-emitting layer 713 with a low heat-resistance.Also, since the DLC film has a high blocking effect against oxygen, theoxidation of the light-emitting layer 713 can be suppressed. Thus, theoxidation of the light-emitting layer 713 during the following sealingprocess can be prevented.

Further, a sealing member 717 is provided on the passivation film 716,and then a cover member 718 is adhered to the sealing member 717.Ultraviolet light cured resin may be used as the sealing member 717, andit is effective to provide a material having a hygroscopic effect or amaterial having an oxidation inhibition effect inside. Also, in thisembodiment, a member in which a carbon film (preferably, a diamondcarbon like film) is formed on both surfaces of, a glass substrate, aquartz substrate, or a plastic substrate (including a plastic film) isused as the cover member 718.

Thus, a light-emitting device of the structure as shown in FIG. 19 iscompleted. Note that, after the formation of the bank 712, it iseffective to successively perform the processes until the formation ofthe passivation film 716 using a film formation apparatus of a multichamber system (or an inline system) without exposing to air. Further,processes until the adhesion of the cover member 718 can be successivelyperformed without exposing to air.

Thus, n-channel TFTs 601 and 602, a switching TFT (n-channel TFT) 603,and a current control TFT (n-channel TFT) 604 are formed on theinsulator 501 in which a plastic substrate is formed as a base. Thenumber of masks required in the manufacturing process until now is lessthan that required in a general active matrix light-emitting device.

That is, the manufacturing process of the TFTs is largely simplified,and thus the improvement of yield and the reduction of a manufacturingcost can be realized.

Further, as described using FIG. 19, when the impurity regionsoverlapped with the gate electrode through the insulating film areprovided, the n-channel type TFT having a high resistant against thedeterioration due to a hot carrier effect can be formed. Thus, thelight-emitting device with high reliability can be realized.

In this embodiment, only the structures of the pixel portion and thedriver circuit are shown. However, according to the manufacturingprocess of this embodiment, logic circuits such as a signal separationcircuit, a D/A converter, an operational amplifier, and a γ-correctioncircuit can be further formed on the same insulator. A memory and amicroprocessor can be also formed.

A light-emitting device of this embodiment after the sealing (filling)process for protecting the light-emitting element will be describedusing FIGS. 20A and 20B. Note that, if necessary, reference symbols usedin FIG. 19 are referred to.

FIG. 20A is a top view representing the state after the sealing of theEL element, and FIG. 20B is a cross sectional view along a line A-A′ ofFIG. 20A. Reference numeral 801 shown by a dotted line denotes a sourceside driver circuit, reference numeral 806 denotes a pixel portion, andreference numeral 807 denotes a gate side driver circuit. Also,reference numeral 901 denotes a cover member, reference numeral 902denotes a first sealing member, and reference numeral 903 denotes asecond sealing member. A sealing member 907 is provided in the insidesurrounded by the first sealing member 902.

Note that, reference numeral 904 denotes a wiring for transmittingsignals inputted to the source side driver circuit 801 and the gate sidedriver circuit 807. The wiring 904 receives a video signal and a clocksignal from an FPC (flexible printed circuit) 905 as an external inputterminal. In FIG. 20A, although only the FPC is shown, a printed wiringboard (PWB) may be attached to the FPC. The light-emitting device inthis specification includes not only the main body of the light-emittingdevice but also the light-emitting device to which the FPC or the PWB isattached.

Next, the cross-sectional structure will be described using FIG. 20B.The pixel portion 806 and the gate side driver circuit 807 are formedover a substrate 700. The pixel portion 806 is formed by a plurality ofpixels each having a current control TFT 604 and a pixel electrode 710electrically connected with the drain region thereof. Also, the gateside driver circuit 807 is formed using the CMOS circuit in which ann-channel type TFT 601 and a p-channel type TFT 602 are combined witheach other (see FIG. 14).

The pixel electrode 710 functions as an anode of the light-emittingelement. Also, banks 712 are formed in both ends of the pixel electrode710. A light-emitting layer 713 and a cathode 714 of the light-emittingelement are formed on the pixel electrode 710.

The cathode 714 also functions as a wiring common to all pixels, and iselectrically connected with the FPC 905 through the connection wiring904. Further, all elements which are included in the pixel portion 806and the gate side driver circuit 807 are covered with the cathode 714and a passivation film 716.

Also, the cover member 901 is adhered to the resultant substrate 700 bythe first sealing member 902. Note that, in order to keep an intervalbetween the cover member 901 and the light-emitting element, a spacermade of a resin film may be provided. Then, the inside of the firstsealing member 902 is filled with a sealing member 907. Note that, it ispreferred that epoxy resin is used as the first sealing member 902 andthe sealing member 907. Also, it is desired that the first sealingmember 902 is a material to which moisture and oxygen are not penetratedas much as possible. Further, a material having a hygroscopic effect ora material having an oxidation inhibition effect may be contained in thesealing member 907.

The sealing member 907 provided to cover the light-emitting element alsofunctions as an adhesive for adhering the cover member 901 to theresultant substrate 700. Also, in this embodiment, FRP(fiberglass-reinforced plastics), PVF (polyvinylfluoride), Mylar,polyester, or acrylic can be used as a material of a plastic substrate901 a composing the cover member 901.

Also, after the adhering of the cover member 901 using the sealingmember 907, the second sealing member 903 is provided to cover sidesurfaces (exposed surfaces) of the sealing member 907. In the secondsealing member 903, the same material as that of the first sealingmember 902 can be used.

By sealing the light-emitting element with the sealing member 907 withthe above structure, the light-emitting element can be completelyshielded from the outside, and penetration of a substance (such asmoisture or oxygen) which prompts deterioration due to oxidation of thelight-emitting layer, from the outside, can be prevented. Thus, thelight-emitting display with high reliability is obtained.

Thus formed light-emitting device have a TFT which is formed by usingthe semiconductor film conducted homogeneous annealing. Therefore,enough operating characteristics and reliability of the above-mentionedlight-emitting device can be obtained. Such light-emitting device can beused as a display portion of various electronic devices.

This embodiment can be performed by freely combining with Embodiments 1to 3.

Embodiment 6

Various semiconductor devices (active matrix type liquid crystal displaydevice, active matrix type light-emitting device or active matrix typeEC display device) can be formed by applying the present invention.Specifically, the present invention can be embodied in electronicequipment of any type in which such an electrooptical device isincorporated in a display portion.

Such electronic equipment is a video camera, a digital camera, aprojector, a head-mounted display (goggle type display), a carnavigation system, a car stereo, a personal computer, or a mobileinformation terminal (such as a mobile computer, a mobile telephone oran electronic book). FIGS. 21A-21F, 22A-22D, and 23A-23C show one of itsexamples.

FIG. 21A shows a personal computer which includes a body 2001, an imageinput portion 2002, a display portion 2003, a keyboard 2004 and thelike. The invention can be applied to the display portion 2003.

FIG. 21B shows a video camera which includes a body 2101, a displayportion 2102, a sound input portion 2103, operating switches 2104, abattery 2105, an image receiving portion 2106 and the like. Theinvention can be applied to the display portion 2102.

FIG. 21C shows a mobile computer which includes a body 2201, a cameraportion 2202, an image receiving portion 2203, an operating switch 2204,a display portion 2205 and the like. The invention can be applied to thedisplay portion 2205.

FIG. 21D shows a goggle type display which includes a body 2301, adisplay portion 2302, arm portions 2303 and the like. The invention canbe applied to the display portion 2302.

FIG. 21E shows a player using a recording medium on which a program isrecorded (hereinafter referred to as the recording medium), and theplayer includes a body 2401, a display portion 2402, speaker portions2403, a recording medium 2404, operating switches 2405 and the like.This player uses a DVD (Digital Versatile Disc), a CD and the like asthe recording medium, and enables a user to enjoy music, movies, gamesand the Internet. The invention can be applied to the display portion2402.

FIG. 21F shows a digital camera which includes a body 2501, a displayportion 2502, an eyepiece portion 2503, operating switches 2504, animage receiving portion (not shown) and the like. The invention can beapplied to the display portion 2502.

FIG. 22A shows a front type projector which includes a projection device2601, a screen 2602 and the like. The invention can be applied to aliquid crystal display device 2808 which constitutes a part of theprojection device 2601 as well as other driver circuits.

FIG. 22B shows a rear type projector which includes a body 2701, aprojection device 2702, a mirror 2703, a screen 2704 and the like. Theinvention can be applied to the liquid crystal display device 2808 whichconstitutes a part of the projection device 2702 as well as other drivercircuits.

FIG. 22C shows one example of the structure of each of the projectiondevices 2601 and 2702 which are respectively shown in FIGS. 22A and 22B.Each of the projection devices 2601 and 2702 is made of a light sourceoptical system 2801, minors 2802 and 2804-2806, a dichroic mirror 2803,a prism 2807, a liquid crystal display device 2808, a phase differenceplate 2809 and a projection optical system 2810. The projection opticalsystem 2810 is made of an optical system including a projection lens.Embodiment 6 is an example of a three-plate type, but it is not limitedto this example and may also be of a single-plate type. In addition,those who embody the invention may appropriately dispose an opticalsystem such as an optical lens, a film having a polarization function, afilm for adjusting phase difference or an IR film in the path indicatedby arrows in FIG. 22C.

FIG. 22D is a view showing one example of the structure of the lightsource optical system 2801 shown in FIG. 22C. In Embodiment 6, the lightsource optical system 2801 is made of a reflector 2811, a light source2812, lens arrays 2813 and 2814, a polarizing conversion element 2815and a condenser lens 2816. Incidentally, the light source optical systemshown in FIG. 22D is one example, and the invention is not particularlylimited to the shown construction. For example, those whose embody theinvention may appropriately dispose an optical system such as an opticallens, a film having a polarization function, a film for adjusting phasedifference or an IR film.

The projector shown in FIGS. 22A to 22D is of the type using atransparent type of electrooptical device, but there is not shown anexample in which the invention is applied to a reflection type ofelectrooptical device and a light-emitting device.

FIG. 23A shows a mobile telephone which includes a body 2901, a soundoutput portion 2902, a sound input portion 2903, a display portion 2904,operating switches 2905, an antenna 2906 and the like. The invention canbe applied to the display portion 2904.

FIG. 23B shows a mobile book (electronic book) which includes body 3001,display portions 3002 and 3003, a storage medium 3004, operatingswitches 3005, an antenna 3006 and the like. The invention can beapplied to the display portions 3002 and 3003.

FIG. 23C shows a display which includes a body 3101, a support base3102, a display portion 3103 and the like. The invention can be appliedto the display portion 3103. The invention is particularly advantageousto a large-screen display, and is advantageous to a display having adiagonal size of 10 inches or more (particularly, 30 inches or more).

As is apparent from the foregoing description, the range of applicationsof the invention is extremely wide, and the invention can be applied toany category of electronic apparatus. Electronic apparatus according tothe invention can be realized by using a construction made of acombination of arbitrary ones of Embodiments 1 to 5.

According to the invention, by forming a laser beam into a linear shapeduring laser annealing, it is possible to improve the throughput oflaser annealing, and in addition, by using a solid-state laser whichenables easy maintenance, it is possible to achieve a greaterimprovement in throughput than can be attained with laser annealingusing an existing excimer laser. Furthermore, it is possible to reducethe manufacturing costs of semiconductor devices such as TFTs or liquidcrystal display devices formed of TFTs.

Moreover, by obliquely irradiating a laser beam onto a semiconductorfilm, it is possible to remove or reduce a concentric-circle patternwhich is formed on the semiconductor film, whereby the properties of thesemiconductor films after laser annealing can be made uniform. Byfabricating the semiconductor device by using such a semiconductor film,it is possible to improve the performance of the semiconductor device toa great extent.

1. A laser irradiation apparatus comprising: a substrate stage; asubstrate over the substrate stage, a semiconductor film being formedover the substrate; and a laser oscillator which irradiates thesemiconductor film with a laser beam, wherein the semiconductor film isirradiated with the laser beam at an incident angle θ, and wherein theincident angle θ satisfiesθ≧arctan(w/(14×D)), (w=(w ₁ +w ₂)/2), where w₁ indicates a beam width ofthe laser beam irradiated onto the semiconductor film, w₂ indicates abeam width of the laser beam at the semiconductor film after reflectedby a back surface of the substrate, and D indicates a thickness of thesubstrate.
 2. The laser irradiation apparatus according to claim 1,wherein the semiconductor film is crystallized by the laser beam.
 3. Thelaser irradiation apparatus according to claim 1, wherein an energydistribution of the laser beam is uniformed by using long focal lengthcylindrical lenses at or near an irradiation plane.
 4. The laserirradiation apparatus according to claim 1, wherein the laser beam islinear in shape at or near an irradiation plane.
 5. The laserirradiation apparatus according to claim 1, wherein the laser beam has awavelength of 350 nm or more.
 6. The laser irradiation apparatusaccording to claim 1, wherein the laser beam has a wavelength of 400 nmor more.
 7. The laser irradiation apparatus according to claim 1,wherein the laser beam is the second harmonic of one kind selected fromthe group consisting of a YAG laser, a YVO₄ laser, a YLF laser, a YAIO₃laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and aglass laser.
 8. A laser irradiation apparatus comprising: a substratestage; a substrate over the substrate stage, a semiconductor film beingformed over the substrate; a laser oscillator which irradiates thesemiconductor film with a laser beam; and a mirror configured to adjusta direction of the laser beam, wherein the semiconductor film isirradiated with the laser beam at an incident angle θ after reflected bythe mirror, and wherein the incident angle θ satisfiesθ≧arctan(w/(14×D)), (w=(w ₁ +w ₂)/2), where w₁ indicates a beam width ofthe laser beam irradiated onto the semiconductor film, w₂ indicates abeam width of the laser beam at the semiconductor film after reflectedby a back surface of the substrate, and D indicates a thickness of thesubstrate.
 9. The laser irradiation apparatus according to claim 8,wherein the semiconductor film is crystallized by the laser beam. 10.The laser irradiation apparatus according to claim 8, wherein an energydistribution of the laser beam is uniformed by using long focal lengthcylindrical lenses at or near an irradiation plane.
 11. The laserirradiation apparatus according to claim 8, wherein the laser beam islinear in shape at or near an irradiation plane.
 12. The laserirradiation apparatus according to claim 8, wherein the laser beam has awavelength of 350 nm or more.
 13. The laser irradiation apparatusaccording to claim 8, wherein the laser beam has a wavelength of 400 nmor more.
 14. The laser irradiation apparatus according to claim 8,wherein the laser beam is the second harmonic of one kind selected fromthe group consisting of a YAG laser, a YVO₄ laser, a YLF laser, a YAIO₃laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and aglass laser.
 15. A laser irradiation apparatus comprising: a substratestage which is inclined from a horizontal direction; a substrate overthe substrate stage, a semiconductor film being formed over thesubstrate; and a laser oscillator which irradiates the semiconductorfilm with a laser beam, wherein the semiconductor film is irradiatedwith the laser beam at an incident angle θ, and wherein the incidentangle θ satisfiesθ≧arctan(w/(14×D)), (w=(w ₁ +w ₂)/2), where w₁ indicates a beam width ofthe laser beam irradiated onto the semiconductor film, w₂ indicates abeam width of the laser beam at the semiconductor film after reflectedby a back surface of the substrate, and D indicates a thickness of thesubstrate.
 16. The laser irradiation apparatus according to claim 15,wherein the semiconductor film is crystallized by the laser beam. 17.The laser irradiation apparatus according to claim 15, wherein an energydistribution of the laser beam is uniformed by using long focal lengthcylindrical lenses at or near an irradiation plane.
 18. The laserirradiation apparatus according to claim 15, wherein the laser beam islinear in shape at or near an irradiation plane.
 19. The laserirradiation apparatus according to claim 15, wherein the laser beam hasa wavelength of 350 nm or more.
 20. The laser irradiation apparatusaccording to claim 15, wherein the laser beam has a wavelength of 400 nmor more.
 21. The laser irradiation apparatus according to claim 15,wherein the laser beam is the second harmonic of one kind selected fromthe group consisting of a YAG laser, a YVO₄ laser, a YLF laser, a YAIO₃laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and aglass laser.
 22. A laser irradiation apparatus comprising: a substratestage; a substrate over the substrate stage, a semiconductor film beingformed over the substrate; and a laser oscillator which irradiates thesemiconductor film with a laser beam, wherein the semiconductor film isirradiated with the laser beam at an incident angle θ, and wherein theincident angle θ satisfiesθ≧arctan(w/(2×D)), (w=(w ₁ +w ₂)/2), where w₁ indicates a beam width ofthe laser beam irradiated onto the semiconductor film, w₂ indicates abeam width of the laser beam at the semiconductor film after reflectedby a back surface of the substrate, and D indicates a thickness of thesubstrate.
 23. The laser irradiation apparatus according to claim 22,wherein the semiconductor film is crystallized by the laser beam. 24.The laser irradiation apparatus according to claim 22, wherein an energydistribution of the laser beam is uniformed by using long focal lengthcylindrical lenses at or near an irradiation plane.
 25. The laserirradiation apparatus according to claim 22, wherein the laser beam islinear in shape at or near an irradiation plane.
 26. The laserirradiation apparatus according to claim 22, wherein the laser beam hasa wavelength of 350 nm or more.
 27. The laser irradiation apparatusaccording to claim 22, wherein the laser beam has a wavelength of 400 nmor more.
 28. The laser irradiation apparatus according to claim 22,wherein the laser beam is the second harmonic of one kind selected fromthe group consisting of a YAG laser, a YVO₄ laser, a YLF laser, a YAIO₃laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and aglass laser.
 29. A laser irradiation apparatus comprising: a substratestage; a substrate over the substrate stage, a semiconductor film beingformed over the substrate; a laser oscillator which irradiates thesemiconductor film with a laser beam; and a mirror configured to adjusta direction of the laser beam, wherein the semiconductor film isirradiated with the laser beam at an incident angle θ after reflected bythe mirror, and wherein the incident angle θ satisfiesθ≧arctan(w/(2×D)), (w=(w ₁ +w ₂)/2), where w₁ indicates a beam width ofthe laser beam irradiated onto the semiconductor film, w₂ indicates abeam width of the laser beam at the semiconductor film after reflectedby a back surface of the substrate, and D indicates a thickness of thesubstrate.
 30. The laser irradiation apparatus according to claim 29,wherein the semiconductor film is crystallized by the laser beam. 31.The laser irradiation apparatus according to claim 29, wherein an energydistribution of the laser beam is uniformed by using long focal lengthcylindrical lenses at or near an irradiation plane.
 32. The laserirradiation apparatus according to claim 29, wherein the laser beam islinear in shape at or near an irradiation plane.
 33. The laserirradiation apparatus according to claim 29, wherein the laser beam hasa wavelength of 350 nm or more.
 34. The laser irradiation apparatusaccording to claim 29, wherein the laser beam has a wavelength of 400 nmor more.
 35. The laser irradiation apparatus according to claim 29,wherein the laser beam is the second harmonic of one kind selected fromthe group consisting of a YAG laser, a YVO₄ laser, a YLF laser, a YAIO₃laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and aglass laser.
 36. A laser irradiation apparatus comprising: a substratestage which is inclined from a horizontal direction; a substrate overthe substrate stage, a semiconductor film being formed over thesubstrate; and a laser oscillator which irradiates the semiconductorfilm with a laser beam, wherein the semiconductor film is irradiatedwith the laser beam at an incident angle θ, and wherein the incidentangle θ satisfiesθ≧arctan(w/(2×D)), (w=(w ₁ +w ₂)/2), where w₁ indicates a beam width ofthe laser beam irradiated onto the semiconductor film, w₂ indicates abeam width of the laser beam at the semiconductor film after reflectedby a back surface of the substrate, and D indicates a thickness of thesubstrate.
 37. The laser irradiation apparatus according to claim 36,wherein the semiconductor film is crystallized by the laser beam. 38.The laser irradiation apparatus according to claim 36, wherein an energydistribution of the laser beam is uniformed by using long focal lengthcylindrical lenses at or near an irradiation plane.
 39. The laserirradiation apparatus according to claim 36, wherein the laser beam islinear in shape at or near an irradiation plane.
 40. The laserirradiation apparatus according to claim 36, wherein the laser beam hasa wavelength of 350 nm or more.
 41. The laser irradiation apparatusaccording to claim 36, wherein the laser beam has a wavelength of 400 nmor more.
 42. The laser irradiation apparatus according to claim 36,wherein the laser beam is the second harmonic of one kind selected fromthe group consisting of a YAG laser, a YVO₄ laser, a YLF laser, a YAIO₃laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and aglass laser.